Transformer structures



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United States Patent 3,151,304 TRANSFORMER STRUCTURES Charley W. Miller, Sharon, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corpora- The invention relates generally to transformers and, more particularly, to cooling systems for high voltage power transformers.

This application is a continuation of applicants application Serial No. 316,108, filed May 27, 1959, and now abandoned, which is a continuation-in-part of applicants parent application Serial No. 672,287, filed July 16, 1957, and now abandoned and assigned to the same assignee as this application.

Heretofore in cooling power transformers, the usual practice has been to separate the pancake coils or windings to provide passageways for cooling mediums such as liquid or gas dielectrics. The voltage between the pancake coils is sometimes quite high and the problem of providing aquate insulation in conjunction with the passageways becomes quite a diflicult one.

The object of the invention is to provide for so constructing a transformer that the insulating values of the solid insulation on the windings will be utilized to best advantage.

It is also an object of the invention to so locate the passageways for a cooling medium in a transformer that the cooling medium acts most effectively.

A further object of the invention is to provide for so locating the passageways for conveying the cooling medium through the coils of a transformer, that the insulating of the coils adjacent the passageways may be easily accomplished.

Other objects of the invention will, in part, be obvious, and will, in part, appear hereinafter.

The invention, accordingly, comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth and scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

FIGURE 1 is a View partly in section and partly in side elevation of a portion of a transformer embody- ,ing the features of the invention;

FIG. 2 is a View taken along the line II-II of FIG. 1;

FIG. 3 is a View taken along the line IIIIII of FIG. 1; and

1 FIGS. 4 and 5 are diagrammatical representations of a portion of the windings of the transformer shown in FIGS. 1, 2 and 3.

Referring now to FIG. 1, a transformer shown generally at is provided with a case 11 of the form-fit type. In form-fit transformer cases, a shelf 12 or other well known similar structural element is provided for supporting the core 13 and coils 9 which make up windings 40 of the transformer 10. This shelf 12 may extend completely around the transformer 10 and since the lower portion of the transformer case 11 is made of :heavy sheet steel, the shelf 12 will support a great weight.

In this particular embodiment of the invention, the core iron 13 is carried by the shelf 12 and a plate 14.

.Blocks 15, usually of wood, are mounted between the Patented Sept. 29, 1964 core iron 13 and the shelf 12. The plate 14 is attached to case 11.

In addition to the supporting structure described, layers of a suitable cellulosic material 18, are located between the core iron 13 and the wall of the case 11. Blocks 19 are fitted on top of the core iron 13 and below a channel member 26, which is attached to the case 11 to hold the core 13 and coils 9 in position.

In the building of power transformers, fiat windings or coils 9 which are usually called pancake coils are employed for both the high and low voltage windings. These large flat coils or windings are wound from conductors 21 generally rectangular in cross section. Further, the coils 9, when finished, are generally rectangular in shape, as shown in FIG. 1.

In order to prevent the flow of eddy currents in the conductors 21, it is common practice in winding these large pancake coils 9 to employ two conductors 21A and 21B arranged in side-by-side relationship. Therefore, each turn of the pankcake coil 9 comprises two insulated conductors 21A and 21B disposed or located physically in side-by-side or parallel relationship and with the two conductors 21A and 21B connectedin parallel circuit relationship. Therefore, examination of the usual pancake coil, such as 9, reveals that it comprises two layers of conductors 21A and 21B which are separated from one another. The voltage therefore between the adjacent layers of conductors 21A and 21B making up a coil 9 is very low or negligible because of the parallel electrical connection of the layers of conductors 21A and 21B of each coil 9, as shown diagrammatically in FIGS. 4 and 5, and circulating currents in coil 9 are reduced because of the conventional conductor transpositions as indicated at 21C in FIG. 5. There is therefore little chance of a breakdown of the insulation between the layers of conductors 21A and 2113.

As shown in FIGS. 4 and 5, the layers of conductors 21A and 21B of each of the pancake coils 9 are connected in parallel circuit relationship while the plurality of pancake coils 9 which make up each winding 40 of transformer 10 are preferably connected in series circult relationship. As best shown in FIGS. 3 and 5, the layers of conductors 21A and 21B which make up each of the pancake coils 9 may be transposed during the winding thereof as indicated at 21C, in any conventional manner to reduce losses due to circulating currents in the closed loop formed by the layers of conductors 21A and 21B which occur because of the extremely small voltage induced between said layers by magnetic leakage flux.

The voltage between adjacent pancake coils 9 is of an entirely different order from the voltage between adjacent layers 21A and 21B in a pancake coil 9. The voltage between adjacent pancake coils 9 may be very high and the amount of insulation required to prevent possible breakdown from one pancake coil 9 to another has to be of substantial proportions, and will depend on the voltage to be insulated against.

The insulation that is ordinarily employed for insulating the pancake coils 9 from one and another and from the core iron 13 and case 11 is usually a cellulosic material.

The big problem in using cellulosic materials occurs at the corner of the coils 9 where it has to be bent. Therefore, when the passageways for the cooling medium are located between the pancake coils 9, the problem of insulating one coil 9 from the other at the corners is a troublesome one.

In the present structure, the applicant has avoided this problem by separating the two layers 21A and 21B of conductors making up the pancake coil 9 and has provided a passageway 22 for the cooling medium within the pancake coil 9 itself. The spacing of the layers of the con- 3 ductors EA and 21B of the pancake coil 9 will depend on the design conditions to be met, that is, the amount of cooling medium that should be circulated and other design requirements.

The pair of conductors 23A and 21B maldng up the pancake coil 9 may be maintained in proper spaced relation by means of a plate 23 carrying a plurality of spacers 24. The plate and spacers 23 and 24, respectively, will be made from some suitable cellulosic material that is commonly supplied by the trade for this purpose. The spacers 24 will be disposed on the plate 23 in some suitable predetermined pattern. The main purpose in employing a predetermined pattern for the spacers 24 is to provide for the proper distribution of the cooling medium as it flows through the passageways to obtain the most effective cooling.

The insu ation of the layers of conductors 21A and 21B making up the pancake coil 9, as pointed out hereinbefore, is a minor problem since the voltage between the layers of conductors 21A and 21B is very low. Further, a cooling medium with low breakdown characteristics may be employed since the voltage to which it is exposed between the layers 231A and 21B is low or negligible. The insulation of one pancake coil 9 from one another is more of a problem since the voltage between the pancake coils 9 is usually rather high. However, in a structure of this type, a mass of solid insulation may now be located between adj cent pancake coils 9 rather than the cooling ducts and liquid or gas insulation which generally can withstand much less voltage stress than solid insulation 3b can Withstand. This solid insulation 3% substantially fills the space between adjacent pancake coils 9 thus substantially reducing the spacing or clearances required between adjacent coils 9 compared to conventional windings which employ cooling ducts and iquid or gas insulation between coils. The use of solid insulation 3% also permits the practical use of higher voltages in a more compact winding construction compared to conventional windings.

In preparing the pancake coils 9, the layers of conductors 21A and 21' will be disposed in spaced relation and the whole coil 9 may be carefully insulated, since no provision need be made for a passageway between the pancake coils 9. The insulation at the corners may be more readily shaped and at less expense. Further, since the insulation 3d between the pancake coils is now one solid mass, the amount of insulation 3% may be reduced since there is no great danger of the insulation 3% breaking down in sections as, for instance, between the one pancake coil 9 and the dielectric liquid in the passageway. The use of insulation 3i as one solid mass between pancake coils 9 will improve the space factor in the transformer 10.

The openings 25 and 26 are provided in the bottom and top respectively of the insulated pancake coils 9 to provide for the entrance and exit of the cooling medium to the layers of conductors 21A and 21B of each of the coils 9 as it circulates in the transformer 10. When the present type of structure is employed, the openings 25 and 26 are disposed as far as possible from the next adjacent pancake coil 9 where the dielectric field has a low intensity and there is little chance of creepage and breakdown between the pancake coils 9. The openings 25 and 26 will also be located as far as practical from the core iron 13, case 11 and supporting structure of the transformer 10 where the dielectric has a low intensity so that the possibility of breakdown between the coils 9 and the core iron 13, case 11 and supporting structure is reduced to a minimum.

It is good practice in building transformers of this type to provide barriers, such as 27, between the windings 40, with the high voltage Winding being shown generally at 29, and the low voltage windings shown at 28. These barriers 27 will be made from suitable cellulosic insulating material well known in the art.

As shown in FIG. 3 for the high voltage winding 29 when pancake coils 9, such as described hereinbefore, are employed and separated from one another at the outside Al. and inside in alternate coils 9, solid insulation 30 will be provided between adjacent pancake coils 9. This assures etter protection against breakdown between the pancake coils 9 at the side where the adjacent coils 9 are not interconnected and where the voltage stress is highest.

it is to be understood that in certain applications, the solid insulation 39 between the adjacent pancake coils 9 may be at least partially impregnated or permeated with the same cooling medium that cools said coils. This cooling medium may be any suitable fluid.

Test information on this type of transformer structure has revealed that it is very desirable and resists breakdown eficctively. Further, there is less possibility of failure even when the liquid dielectrics employed as cooling mediums become contaminated.

Since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A transformer comprising a magnetic core, a core supporting structure, a cooling medium, a case for the core supporting structure and cooling medium, pancake coils comprising a plurality of layers or" conductors, the layers of conductors being spaced from one another along a common axis to provide ducts therebetween for the cooling medium to flow in contact with the coils, said layers of conductors being connected in parallel circuit relationship so that the potential diiierence between the conductors on opposite sides of each of the ducts is negligible, thus permitting a cooling medium of low insulating value to be circulated between the layers of conductors to cool the transformer without danger of breakdown, said pancake coils being connected in series circuit relationship, and solid insulation of high insulating value disposed to substantially fill the space between adjacent pancake coils to prevent breakdown between the pancake coils when the potential difference between the pancake coils is high.

2. A transformer for utilizing a cooling medium, comprising, a plurality of spirally wound coils, each spirally wound coil comprising a plurality of spirally wound conductors electrically connected in parallel to limit the volt age therebetween to a negligible value and spaced from one another along a common axis to provide passageways between them for a cooling medium and solid insulation substantially enclosing the spirally wound coils and substantially filling the space between the coils, the solid insulation having openings therein to give the cooling medium access to the passageways between the spaced conductors of the coil.

3. A transformer utilizing a fluid cooling medium comprising, a plurality of spirally wound coils connected in series circuit relationship, each spirally wound coil comprising a plurality of layers of spirally wound conductors spaced from one another along a common axis to provide passageways between them for a cooling medium, said layers of conductors of each coil being electrically connected in parallel circuit relationship, and solid insulation substantially enclosing the spirally wound coils and substantially filling the space between the coils, the solid insulation having openings therein to give the cooling medium access to the passageways between the spaced conductors of the coil.

4. In a transformer utilizing a cooling medium, in combination, a plurality of spirally wound coils connected in series circuit relationship, each spirally wound coil comprising a plurality of layers of spirally wound conductors spaced from one another along a common axis to provide passageways between them for a cooling medium, means for maintaining the spirally wound conduc tors in spaced relationship to keep the passageways open for the cooling medium and solid insulation substantially enclosing the spirally wound coils and substantially filling the space between the coils, said layers of conductors of each coil being electrically connected in parallel circuit relationship to limit the voltage therebetween to a negligible value, the solid insulation having openings therein to give the cooling medium access to the passageways between the spaced conductors of the coil.

5. In a transformer provided with a core and a core supporting structure therefor disposed in a case and adapted to be cooled by a cooling medium, in combination,a plurality of spirally wound coils mounted on the core and connected in series circuit relationship, each spirally wound coil comprising a plurality of layers of spirally wound conductors spaced from one another along a common axis to provide passageways between them for the cooling medium, solid insulation substantially enclosing the spirally wound coils and substantially filling the space between the coils, said layers of conductors of each coil being electrically connected in parallel circuit relationship to limit the voltage therebetween to a negligible value, the solid insulation having openings at points as remote as possible from the core iron, case and supporting structure to restrict breakdown from the coils to the core, case and supporting structure.

6. A transformer comprising a magnetic core, a supporting structure, a cooling medium, a case for the core, supporting structure and cooling medium, a plurality of spirally wound pancake coils mounted on the core and connected in series circuit relationship, each spirally wound pancake coil comprising a plurality of spirally wound layers of conductors spaced from one another along a common axis to provide a passageway between them for the cooling medium, means for maintaining the layers of spirally wound conductors in spaced relationship and the passageway open for the cooling medium, solid insulation substantially enclosing the spirally wound pancake coils and substantially filling the space between the coils, said layers of conductors of each coil being electrically connected in parallel circuit relationship, the solid insulation having openings at points as remote as possible from the core, case and supporting structure to restrict creepage between the pancake coils and the core and supporting structure.

7. A transformer comprising a magnetic core, a supporting structure, a cooling medium, a case, a plurality of spirally wound pancake coils mounted on the core, each spirally wound pancake coil comprising a plurality of layers of spirally wound conductors spaced from one another along a common axis to provide passageways between them for the cooling medium, spacers disposed between the layers of the spirally wound coils to keep them separated and the passageway open for the cooling medium, the spacers being so disposed that the cooling medium will be distributed over the spirally wound coils as it flows through the passageways, solid insulation applied to the spirally wound coils and substantially filling the space between them, said layers of conductors of each coil being electrically connected in parallel circuit relationship to limit the voltage therebetween to a negligible value, the solid insulation having openings therein to' permit the cooling medium to enter and leave the passageways, the openings in the solid insulation being disposed at points as remote as possible from the case and supporting structure to cooperate in preventing creepage from the pancake coils to the case and supporting structure and between the pancake coils.

8. A transformer comprising a magnetic core, a supporting structure, a cooling medium, a case for the core supporting structure and cooling medium, a plurality of pancake coils each comprising a plurality of layers of conductors, said pancake coils being connected in series circuit relationship, the layers of conductors of each coil being spaced from one another along a common axis to provide ducts for the cooling medium to How in contact with the coil, said layers of each pancake coil being electrically connected in parallel circuit relationship to limit the voltage across each of said ducts to a negligible value, the potential diiference between the conductors on opposite sides of the ducts being negligible, whereby a cooling medium of low insulating value may be employed to cool the transformer without danger of breakdown, and solid insulation of high insulating value disposed between the pancake coils to prevent breakdown between the pancake coils when the potential difference between the pancake coils is high.

9. A transformer comprising a magnetic core, a supporting structure, a cooling medium, a case for the core, supporting structure and cooling medium, a plurality of pancake coils, each coil comprising a plurality of layers of spirally wound conductors electrically connected in parallel circuit relationship, the layers of spirally wound conductors being spaced from one another along a common axis to provide passageways for the cooling medium, solid insulation disposed around each pancake coil and substantially filling the space between the pancake coils, the solid insulation around the pancake coils having openings therein to give the cooling medium access to the spirally wound layers of coils, the openings being located as remote as possible from the case and supporting structure to prevent creepage between the pancake coils and the supporting structure and case and between the adjacent pancake coils.

10. A transformer comprising a magnetic core, supporting structure for the core, a cooling medium, a case for the core, supporting structure and cooling medium, a plurality of pancake coils, each pancake coil comprising a plurality of layers of spirally wound conductors disposed in space relation along a common axis to provide a passageway for the cooling medium, said layers of spirally wound conductors being electrically connected in parallel circuit relationship to limit the potential difference therebetween to a negligible value, solid insulation applied to the layers of spirally wound conductors and substantially filling the space between the pancake coils, and spacers disposed between the layers of spirally wound conductors to maintain them in spaced relationship along a common axis and the passageway open for the cooling medium, the spacers being so disposed as to effect efficient cooling, the solid insulation applied to the layers of conductors having openings therein to give the cooling medium access to the passageways, the openings being disposed as remote as possible from the supporting structure and case to restrict creepage between the pancake coils and supporting structure and case and between adjacent pancake coils.

11. A transformer comprising a magnetic core, supporting structure, a cooling medium, a case for the core, supporting structure and cooling medium, high and low voltage coils disposed on the core, a plurality of pancake coils in each of the high and low voltage windings, the coils of each winding being electrically connected in series circuit relationship, each pancake coil comprising a plurality of layers of spirally wound conductors, the layers of the spirally wound conductors being spaced from one another along a common axis to provide passageways for the cooling medium, said layers of spirally wound conductors being electrically connected in parallel circuit relationship, solid insulation disposed around each pancake coil and substantially filling the space between the pancake coils, the solid insulation around the pancake coils having openings therein to give the cooling medium access to the spirally wound layers of coils, the openings being located as remote as possible from the case and supporting structure to prevent creepage between the pancake coils and the supporting structure and case and between adjacent pancake coils, and solid insulation between the high and low voltage windings.

12. A transformer comprising a magnetic core, a support structure, a cooling medium, a case for the core, supporting structure and cooling medium, high and low voltage coils disposed on the core, a plurality of pancake coils in each of the high and low voltage windings, each aaansea s pancake coil comprising a plurality of layers of spirally wound conductors, the layers of the spirally Wound conductors being spaced from one another along a common axis to provide passageways for the cooling medium and electrically connected in parallel circuit relationship to limit the voltage therebetween to a negligible value, solid insulation disposed around each pancake coil and substantially filling the space between the pancake coils, the solid insulation around the pancake coils having openings therein to give the cooling medium access to the spirally wound layers of coils, the openings being located as remote as possible from the case and supporting structure to prevent creepage between the pancake coils and the supporting structure and case and between adjacent pancake coils, and solid insulation completely filling the space between the high voltage and low voltage windings.

13. A transformer utilizing a fluid cooling medium, comprising a plurality of spirally wound coils connected in series circuit relationship, each spirally wound coil comprising a plurality of layers of spirally wound conductors spaced from one another along a common axis to provide passageways between them for a cooling medium, said layers of conductors of each coil being electrically connected in parallel circuit relationship to limit the voltage therebetween to a negligible value, and solid insulation substantially enclosing the spirally Wound coils and substantially filling the space between the coils, the layers of conductors of at least one of said coils being transposed during the winding thereof, the solid insulation having openings therein to give the cooling medium access to the passageways between the spaced conductors of the coil.

References (Iited in the tile of this patent UNlTED STAT-ES PATE TS Re. 14,891 Johannesen June 22, 1920 508,655 Thomson Nov. 14, 1893 

1. A TRANSFORMER COMPRISING A MAGNETIC CORE, A CORE SUPPORTING STRUCTURE, A COOLING MEDIUM, A CASE FOR THE CORE SUPPORTING STRUCTURE AND COOLING MEDIUM, PANCAKE COILS COMPRISING A PLURALITY OF LAYERS OF CONDUCTORS, THE LAYERS OF CONDUCTORS BEING SPACED FROM ONE ANOTHER ALONG A COMMON AXIS TO PROVIDE DUCTS THEREBETWEEN FOR THE COOLING MEDIUM TO FLOW IN CONTACT WITH THE COILS, SAID LAYERS OF CONDUCTORS BEING CONNECTED IN PARALLEL CIRCUIT RELATIONSHIP SO THAT THE POTENTIAL DIFFERENCE BETWEEN THE CONDUCTORS ON OPPOSITE SIDES OF EACH OF THE DUCTS IS NEGLIGIBLE, THUS PERMITTING A COOLING MEDIUM OF LOW INSULATING VALUE TO BE CIRCULATED BETWEEN THE LAYERS OF CONDUCTORS TO COOL THE TRANSFORMER WITHOUT DANGER OF BREAKDOWN, SAID PAN- 